1. Field of the Invention
The present invention relates to a video signal reproduction apparatus for reproducing a video signal, and more particularly, to a video signal reproducing apparatus suited to reproduce a composite video signal, (like a MUSE signal, having an image region and a non-image region) from a recording medium and to restore the video signal.
2. Description of the Related Art
A VTR (video tape recorder) for recording and reproducing video signals generally employs the FM (frequency modulation) method, which is also used to record high-definition signals.
FIG. 1 shows a reproduction portion of a well-known type of VTR, and FIG. 2 shows the detailed construction of a drop-out compensator in FIG. 1. Referring to FIG. 1, a video signal reproduced by a head 40 is amplified by an amplifier 41, and a DC component is removed from the video signal by a HPF (high-pass filter) 42. The waveform of the video signal is equalized by an equalizer 43, and then the video signal is output to a drop-out compensator 44 which is illustrated in detail in FIG. 2. If a drop-out of the video signal arises from dust and so on between a tape and the head 40 in the reproduction process, the drop-out is compensated as a RF (high frequency) signal by the drop-out compensator 44.
The drop-out compensator 44 will now be explained with reference to FIG. 2. The RF signal equalized by the equalizer 43 is input through an input terminal 401, and the drop-out is detected by a drop-out detection circuit 402. The drop-out detection circuit 402 detects the drop-out by comparing an envelope level of the RF signal with a predetermined threshold level.
If the drop-out detection circuit 402 does not detect any drop-out, a flag output from the drop-out detection circuit 402 is set at "0", and the RF signal input through the input terminal 401 is selected by a selector 403 and output through a 1H delay line 404. On the other hand, if the drop-out detection circuit 402 detects the drop-out, a flag output from the drop-out detection circuit 402 is set at "1", and a RF signal having a great correlation to an image on a previous line delayed by the 1H delay line 404 is selected by the selector 403 and output through the 1H delay line 404. The drop-out portion is thus compensated.
Returning to FIG. 1, the amplitude of the RF signal whose drop-out is compensated by the drop-out compensator 44 is limited by a limiter 45, the RF signal is demodulated by a FM demodulator 46, and a high-frequency component is removed from the RF signal by a LPF (low-pass filter) 47. Subsequently, a frequency region emphasized in recording is returned to an initial level by a de-emphasis circuit 48, noise is removed by a noise reduction circuit 49, and the RF signal is output as a video signal.
However, if the drop-out is detected in the above conventional video signal reproduction apparatus, compensation is performed by a signal having a great correlation to the image in the previous line. Therefore, when a MUSE signal is reproduced, since the MUSE signal includes signals having no correlation between lines, such as an audio signal, control signals, and VITS (vertical interval test signals), besides image signals (C image, Y image) as shown in FIG. 3, the audio signal is also compensated by a signal in the previous line, and thus it is feared that an audio signal which should not be heard is output. However, if the above drop-out compensation is not performed, the image is remarkably deteriorated.
In particular, if a succession of drop-outs occurs in a plurality of lines in front of and behind a boundary between an audio signal and an image signal, the image signal is replaced with a signal other than an image signal. This case results in a great deterioration of an output image.